Such a device is described, for example, in U.S. Pat. No. 4,597,093, issued June 24, 1986. In this patent, it is possible to look through the viewing microscope 78 and observe the under side 92 of the coating 93 which is illuminated by a light source 94. The coating lies on a working panel 18 which can be moved in the direction 24 and/or 26 by a precision transmission 27, 29. The working panel 18 is relatively small. Relatively large objects would hang down below the working panel 18 and would not have a rugged support because the panel 17 is of course lower down than the working panel 18.
The coating can also move while one is working on the instrument table, if something falls against the table or if by chance a garment fouls the device or the latter is struck by the knee or by a chair falling over or suffers similar mishaps.
It can, however, also happen that the object to be measured will in course of time creep or internal stresses may become noticeable so that the object moves like a transparency and so alters its position.
The device is not suitable for rapid and thus economic viewing of printed circuit boards which have to be pushed quickly back and forth over the clearance hole. Aligning the object to be measured with the geometrical longitudinal axis 32 is carried out by a single eye since a stereomicroscope would be too expensive. If the object to be measured is moved quickly, then the eye tires within a short time.